Method to synchronise data and a transmitter and a receiver realising said method

ABSTRACT

A method to realise synchronisation in a receiver (RX), of data (DAT) sent from a transmitter (TX) to the receiver (RX), with a signal (SIG) available in the receiver (RX). The method includes the following steps:  
     in the receiver (RX) generating trigger signals (T) from the signal (S);  
     sending the trigger signals (T) from the receiver (RX) to the transmitter (TX);  
     upon receipt of the trigger signals (T) by the transmitter (TX) sending the data (DAT) from the transmitter (TX) to the receiver (RX).

[0001] The present invention relates to a method to synchronise data asdescribed in the preamble of claim 1, and a transmitter and a receiverrealising said method as described in the preambles of claim 4 and claim6.

[0002] Such a method to synchronise data is common knownledge. Indeed,e.g. in communication systems where data is sent from a transmitter to areceiver, for the receiver to be able to interprete the received data,the received data have to be synchronised in the receiver with areference signal, usual a clock signal of the receiver. Realisingsynchronisation implies more complexity and therefore there is a needfor additional hardware or software in the receiver. The trade-offs aregenerally between expense and complexity, on one hand, and errorperformance on the other hand. However, some kind of receivers e.g.receivers using asymmetric digital subscriber line technology arerequired to have both, a low complexity and also a low errorperformance.

[0003] An object of the present invention is to provide a method tosynchronise data and a transmitter and a receiver realising said methodof the above known type but which are suited for use in communicationsystems where a low complexity and a low error performance are requiredat the receiving side of the communication system.

[0004] According to the invention, this object is achieved by the methodto synchronise data as described in claim 1, and the transmitter and thereceiver realising the method as described in claim 4 and claim 6,respectively.

[0005] Indeed, due to the trigger signals generated from the signalavailable in the receiver and sent to the transmitter, the transmitteris able to send the data to the receiver upon receipt of the triggersignals i.e. at the right time to ensure synchronisation between thedata received in the receiver and the available signal e.g. a clocksignal in the receiver. In this way, the complexity of thesynchronisation process is moved from the receiver side to thetransmitter side of the communication system and each level ofsynchronisation can be realised with the required level of errorperformance and without making the receiver too complex.

[0006] Another characteristic feature of the present invention is thatthe data, sent from the transmitter to the receiver, is asynchronousdata. Indeed, upon receipt of the trigger signals, the transmitter mustbe able to send data even if the trigger signals are sent in anasynchronous way. This is for instance the case when the receiver has toreceive the data at a time moment at which the data has just to fit at apredefined place in a frame. In this way frame synchronisation isachieved.

[0007] Yet another charaderistic feature of the present invention isthat in the event that no data is available in the transmitter to besent upon receipt of the trigger signals, the transmitter is able togenerate idle data and to send this idle data to the receiver. In thisway, e.g. the frame synchronisation proces is not disturbed. This isdescribed in the method of claim 3 and the transmitter of claim 8.

[0008] An important application of the present invention is that thereceiver is included in an asymmetric digital subscriber line (ADSL)modem. This is described in claim 5. In such receiver, the received datais framed into an asymmetric digital subscriber line frame and sent overtwisted pair. However in known ADSL modems using the knownsynchronisdtion methods, when the modem receives data at a higherfrequency than the frequency at which the data is sent, the data has tobe buffered before being framed. As already mentioned above, it isimportant to keep the complexity of a receiver in such a modem low. Byusing the method of the invention, the asymetric digital subscriber linemodem gets rid of the buffering aspect. In fact the buffering is againmoved from the receiver to the transmitter which now must be able tobuffer the data until he receives a trigger signal of the receiver tohove the permission to sent the data to the receiver. Therefore, thisway of synchronising is expecially suited for systems wherein there isanyway buffering foreseen at the transmitting side, e.g. forAsynchronous Transmission Mode (ATM) systems.

[0009] The above mentioned and other objects and features of theinvention will become more apparent and the invention itself will bebest understood by referring to the following description of anembodiment taken in conjunction with the accompanying FIGURE which is ablock scheme of a synchronisation system including a transmitter and areceiver realising the method of the invention.

[0010] Referring to the FIGURE, the working of the synchronisationsystem will be described. First, the working of the synchronisationsystem will be explained by means of a functional description of theblocks shown in the FIGURE. Based on this description implementation ofthe functional blocks will be obvious to a person skilled in the art andwill therefor not be described in detail. In addition, the principleworking of the synchronisation system will be described in furtherdetail.

[0011] The synchronisation system includes a transmitter TX and anasymmetric digital subscriber line modem (ADSL modem) ADSL.

[0012] The transmitter TX includes four functional blocks

[0013] a buffer BUF;

[0014] an idle data generating means ID-GEN

[0015] a data sending means DAT-SEND; and

[0016] a trigger receiving means T-RX.

[0017] The buffer BUF is included to buffer the data DAT presented tothe transmitter TX. This data DAT can be digital data of any kind,however, for this embodiment the data DAT is asynchronous data i.e. dataorganised following the asynchronous transfer mode (ATM) technique. Asmentioned, the buffer BUF buffers the data DAT presented to thetransmitter TX. However, it has to be understood that the buffer BUFwill only do this when it is nessary i.e. when the transmitter receivesmore data DATA then he is allowed to send.

[0018] The idle data generating means ID-GEN is included to generateidle data. It has to be remarked that this one of the typical ATMfunctionalities. Idle data is send whenever there is no informationavailable at the side of the sender at the moment of transmission. Theyallow a full asynchronous operation of both sender and receiver.

[0019] The data sending means DAT-SEND is included to send data from thetransmitter TX to the ADSL modem. This data can be useful userinformation i.e. the data DAT coming from the buffer BUF or idle data,coming from the idle data generating means ID-GEN.

[0020] The trigger receiving means T-RX is included to receive triggersignals T coming from the ADSL modem. Upon receipt of such a triggersignal, the data sending means DAT-SEND is on his turn triggered by thetrigger receiving means T-RX and is allowed to send data.

[0021] The ADSL modem includes besides a receiver RX also thecharacteristic functional blocks of an ADSL modem. Since the descriptionof the ADSL technology goes beyond the scope of this invention, thesefunctional blocks are not shown in the FIGURE. However, it is worth tomention here that one of the functional blocks of such an ADSL modem isa framer which organizes overhead information and user information i.e.the incoming data DAT into ADSL frames, i.e. uniformly sized groups ofbits used to organize the ADSL data stream.

[0022] The receiver RX includes three functional blocks

[0023] trigger generating means T-GEN;

[0024] trigger sending means T-SEND; and

[0025] data receiving means DAT-RX.

[0026] The trigger generating means T-GEN is included to generatetrigger signals T from an available signal SIG in the receiver RX. Thisavailable signal SIG is generated in accordance with the time momentswhenever data DAT is needed to fit into an available ADSL frame on apredetermined place. This signal S is not necessary a clock signal.Indeed, looking to the form of an ADSL frame, not the whole frame mustbe filled with data DAT, so by consequence, the signal S is not a signalwith a constant frequency.

[0027] It has to be remarked here that the trigger signals T are allowedto be of any kind e.g. one single bit pulse or a predefined codeword aslong as the trigger generating means T-GEN of the receiver RX and thetrigger receiving means T-RX of the transmitter TX are lined up witheach other.

[0028] The trigger sending means T-SEND is included to send the triggersignals T from the receiver RX to the transmitter TX and the datareceiving means DAT-RX is included to receive the data DAT coming fromthe transmitter TX.

[0029] The transmission medium for sending the trigger signals is in theFIGURE depicted as a separate line to simplify the description of theworking of the system. However these signals can (and usually are)transmitted over the same transmission medium, i.e. twisted pair, as thedata.

[0030] The principle working of the synchronisation system will bedescribed in the following paragraph.

[0031] Whenever data DAT is needed to fit in an available ADSL frame ona predetermined place, a trigger signal T is generated from theavailable signal SIG and transmitted to the transmitter TX. Upon receiptof a trigger signal T the trigger receiving means T-RX gives a signal tothe data sending means DAT-SEND, e.g. by means of a controle signal, andDAT-SEND on his turn requests data DAT to the buffer BUF. When there isdata DAT available in the buffer BUF, the data DAT is provided to thedata sending means DAT-SEND. However, when no data DAT is available inthe buffer, the synchronisation process may not be disturbed and thedata sending means DAT-SEND requests idle data to the idle datagenerating means ID-GEN. The data, either user data or idle data, issent to the receiver RX and arrives there at the right moment to fitimmediately into the ADSL frame on the predetermined place wherebysynchronisation is established between the data DAT and the availablesignal SIG.

[0032] It has to be remarked that upon receipt of a trigger signal T,the transmitter TX has to send data DAT to the receiver RX. Sending datacan be done immediately after receiving of the trigger signal T, howeverthe invention is not restricted to such kind of synchronisation systemsbut is also applicable for synchronisation systems where the data DAT isonly sent after a predetermined period. Indeed, in this particularembodiment, the total period between the moment of generating aparticular trigger and the moment of data DAT arriving at the receiverRX to fit into a according predefined ADSL frame must be taken intoaccount at initialisation time. It can be necessary to have apredetermined waiting period somewhere in the loop in order to be ableto realise the synchronisation. Since the complexity is moved from thereceiver RX to the transmitter TX, this waiting period will also berealised by the transmitter TX.

[0033] It has to be remarked that due to the cell structure of the ATMdata stream whenever idle data, not corresponding to a complete idlecell has been sent, that upon receipt of subsequent trigger signals Tidle data has to be sent until the complete idle cell is transmitted,even if in the mean time some data DAT becomes available in the bufferBUF.

[0034] While the principles of the invention have been described abovein connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation on the scope of the invention.

1. A method to realise synchronisation in a receiver (RX), of data (DAT)sent from a transmitter (TX) to said receiver (RX), with a signal (SIG)available in said receiver (RX), characterised in that said methodincludes the steps of: in said receiver (RX) generating trigger signals(T) from said signal (SIG); sending said trigger signals (T) from saidreceiver (RX) to said transmitter (TX); upon receipt of said triggersignals (T) by said transmitter (TX) sending said data (DAT) from saidtransmitter (TX) to said receiver (RX).
 2. The method according to claim1, characterised in that said data (DT) is asynchronous data.
 3. Themethod according to claim 1, characterised in that said method furtherincludes in the event that no data is available in said transmitter (TX)to be sent upon receipt of said trigger signals, sending idle data fromsaid transmitter (TX) to said receiver (RX).
 4. A receiver (RX) forreceiving from a transmitter (TX) data (DAT), said data (DAT) having tobe synchronous with a signal (SIG) available in said receiver (RX),characterised in that said receiver (RX) includes: trigger generatingmeans (T-GEN) to generate trigger signals (T) from said signal (SIG);trigger sending means (T-SEND) to send said trigger signals (T) fromsaid receiver (RX) to said transmitter (TX); data receiving means(DAT-RX) to receive said data (DAT) sent by said transmitter (TX) uponreceipt of said trigger signals (T) to said receiver (RX).
 5. Thereceiver (RX) according to claim 4, characterised in that said receiver(RX) is included in an asymmetric digital subscriber line modem.
 6. Atransmitter (TX) for transmitting data (DAT) to a receiver (RX), saiddata (DAT) having to be synchronous with a signal (SIG) available insaid receiver (RX), characterised in that said transmitter (TX) includestrigger receiving means (T-RX) to receive trigger signals T), generatedby said receiver (RX) from said signal (SIG) and sent from said receiver(RX) to said transmitter (TX); data sending means (DAT-SEND) to senddata (DAT) from said transmitter (TX) to said receiver (RX) upon receiptof said trigger signals (T).
 7. The transmitter (TX) according to claim6, characterised in that said transmitter (TX) includes means to sendsaid data (DAT) in an asynchronous way.
 8. The transmitter (TX)according to claim 6, characterised in that said transmitter (TX)includes idle data generating means (ID-GEN) to generate idle data andto send said idle data from said transmitter (TX) to said receiver (RX)in the event that no data (DAT) is available in said transmitter (TX)upon receipt of said trigger signals (T).